Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

The feasibility of using plasma electrolytic treatment to improve the wear resistance of R6M5 high-speed steel has been demonstrated by combining anodic nitriding at 550°C with air quenching from 1230°C and subsequent three-stage tempering at 555°C. Structural and phase transformations in the surface layers of the steel after high-temperature air quenching and three-stage tempering, as well as their influence on tribological behavior in a friction pair with hardened tool steel, were studied using X-ray diffraction and scanning electron microscopy. The most pronounced reduction in the friction coefficient (by a factor of 3) and in weight loss due to wear (by a factor of 11), compared with the untreated sample, occurs after 10 min of nitriding followed by quenching and tempering under oxidative wear conditions observed at a load of 10 N and a sliding speed of 1.44 m/s. The modified layer of nitrided steel after tempering exhibits a finely dispersed structure of high-alloy martensite retaining part of the austenite and containing inclusions of iron, vanadium, and chromium nitrides, as well as tungsten carbide, with a microhardness reaching 1240 HV. At both lower and higher sliding speeds in the studied friction pairs, wear is dominated by fatigue mechanisms involving dry friction and plastic contact.

For the synthesis of composites based on the MAX-phase Ti₃SiC₂, various approaches based on heat treatment and consolidation of powder mixtures 3Ti/1.8SiC/0.8C and 2Ti/1.2SiC/1.8TiC have been considered. The first approach consists in powder heat treatment by vacuum sintering at 1400°C for 1 h and spark plasma sintering at 1350°C and a pressure of 50 MPa. The second approach consists in two-stage heat treatment, including additional consolidation by spark plasma sintering of vacuum-sintered composites. For each of the approaches, the effect of temperature and holding time during spark plasma sintering on the phase composition, density, and porosity of the obtained composites has been determined. It has been found that the consolidation of Ti₃SiC₂–TiC–Ti₅Si₃–TiSi₂ and Ti₃SiC₂–TiC composites obtained by vacuum sintering and spark plasma sintering with the addition of 5 wt % of SiC leads to the formation of high-density Ti₃SiC₂–TiC–TiSi₂ composites with an open porosity index of up to 0.3% and MAX-phase content from 9 to 33 vol % depending on the sintering temperature (1300–1400°C). It has been shown that the microstructure of the composite surfaces synthesized by spark plasma is represented by agglomerates of MAX-phase grains of Ti₃SiC₂, TiC, and inclusions of secondary phases (SiC and Ti₅Si₃ depending on the sintered composition).

The paper explores the capabilities of modern methods of spectral-temporal analysis in studying high-frequency emission from stationary plasma thrusters. The experimental model of SPT-70 developed at the Research Institute of Applied Mechanics and Electrodynamics, Moscow Aviation Institute (RIAME MAI) was chosen as the object of study. The task posed in the study was to test the hypothesis that the considered time sample functions of the emission process can represent a superposition of independent processes intersecting in time and having similar frequency characteristics. Spectral analysis methods such as continuous wavelet transform, Wigner-Ville transform, and empirical mode decomposition were used. The results of the study showed that the integrated use of spectral-temporal analysis methods allows for the further identification of the fine structure of pulsed emission and the acquisition of new knowledge about the nature of the self emission from of plasma thrusters. The obtained data can be used to refine models of electromagnetic emission from stationary plasma thrusters, as well as in the development of signal processing algorithms aimed at increasing the noise immunity of on-board radio systems and ensuring electromagnetic compatibility of spacecraft.

The most important condition for the stable operation of controlled thermonuclear fusion facilities is solving the “first wall” problems, which include the analysis of the interaction between thermonuclear plasma and in-vessel materials. Within this framework, the most pressing issue is the analysis of depths profiles of structural materials interacting with the plasma. This task is related to the fact that to reduce the average atomic number of the elements entering the plasma discharge, coatings made of low atomic number materials, such as lithium and boron, are used on plasma-facing components. This work presents a methodology for reflected electron spectroscopy that enables the depths profiles analysis of targets with complex composition based on the interpretation of differential energy and angle spectra of reflected electrons. A method for calculating the energy spectra of electrons reflected from multicomponent heterogeneous targets is introduced, based on the method of partial intensities, which has been repeatedly tested in numerous studies. Path length distribution function, which is the basis for the method of partial intensities and previously determined only within the framework of Monte Carlo simulations, has been established within an analytical approach. It is noted that to identify the depths profile of the distribution of components in the investigated target, a fitting procedure is employed, which is based on repeatedly solving the forward problem of calculating spectra of electrons reflected from a target of complex composition. A good agreement between the calculations and experimental results has been demonstrated. The simplicity of the experimental implementation of the reflected electron spectroscopy method is emphasized, as it does not require high-energy resolution equipment, since information about the target is extracted from the dome part of the reflected electron spectrum.

This work aims to address the problem of improving the accuracy of thin-film resistors. The main cause of this issue is the uncontrolled change in resistor resistance over time and under the influence of temperature, which makes it difficult to achieve high resistance stability. To solve this problem, the use of compensation layers with temperature coefficients of resistance of opposite signs is proposed. A design and technological solution has been developed for ultra-precision multilayer and combined thin-film resistive structures with temperature self-compensation, made of metal–silicide alloys and nichrome-based alloys, as well as K-30S cermet and nickel, respectively. The combination of films made of Kh20N75Yu alloy and K-30S cermet was chosen based on the optimal ratio of layer thicknesses. The structure and topology of combined and multilayer thin-film resistors have been developed. A technological process for manufacturing thin-film chip resistors has been created; deposition modes and topology formation by photolithography followed by temperature stabilization have been refined. Functional tests of a pilot batch of samples have been carried out, for which additional technological equipment was developed. The developed technology makes it possible to achieve a temperature coefficient of resistance of ±5 × 10^–7 °C^–1 in the operating temperature range from ‒60 to +125°C. The scientific novelty of this work lies in the ability to combine thin films of Kh20N75Yu/K-30S for multilayer and K-30S/Ni for combined resistive structures in the proposed design to achieve temperature compensation and improve stability characteristics.

We studied the kinetics of changes in the diffuse reflectance spectra and the integral absorption coefficient of solar radiation of the original CaSiO₃ powder with µ-sized grains and modified with CeO₂ nanoparticles at their optimal concentration of 3 wt % under electron irradiation (energy E = 30 keV, fluence Φ = (1–7) × 10¹⁶ cm^–2) and the possibility of recording these properties in a vacuum at the irradiation site (in situ). Modification was found to lead to an increase in radiation resistance from 2.39 to 2.89 times depending on the electron fluence. The modification efficiency increases with increasing electron fluence during irradiation. The obtained results can be used to develop new radiation-resistant thermal control coatings of the “optical solar reflectors” class for spacecraft.

We have explored the influence of combined sintering modes on the structural-phase state, density, microhardness and internal structure of ceramics based on yttrium oxide-stabilized zirconium oxide (Y‑PSZ). The combined sintering was carried out using two methods: traditional thermal sintering at atmospheric pressure and electron beam sintering in the forevacuum pressure range. Our results indicate that the temperature of preliminary thermal sintering significantly affects the ceramic properties. The greatest change in density is achieved at a pre-sintering temperature of more than 700°C. X-ray diffraction analysis reveals an increase in the percentage of tetragonal phase and a decrease in cubic and monoclinic phases with increase in temperature of subsequent sintering using an electron beam. The density was 92.2% of the theoretical value at a sintering temperature of 1450°C. The microhardness of the surface reaches 16 GPa and is practically independent of pre-sintering temperature.

The paper presents the results of theoretical and experimental studies of establishing the patterns of phase formation under vacuum heating conditions. The mathematical model includes the heat balance equation and kinetical equation system for eleven chemical reactions. The law of acting masses and Arrhenius law are used to write the kinetical equations. Semi–empirical methods are employed to calculate formal-kinetical parameters. The multiphase product forms in experiment and in numerical model. The numerical calculations obtained qualitatively agree with the experimental results.

The effect of preliminary He⁺ ion implantation on the morphology and microhardness of the surface of vanadium alloy V–10Ti–6Cr–0.05Zr–0.1Si upon subsequent exposure to high-power pulsed laser radiation has been studied. Low-activation vanadium-based structural materials are the most corrosion-resistant with respect to Li. They are promising for reactors with a liquid blanket version, where lithium is a coolant and tritium is a reproducible material. Helium ion implantation into alloy has been carried out in an ion-beam accelerator. General patterns of surface destruction have been established for both the original samples and those preirradiated with helium: formation of a hole surrounded by a breastwork and a heat-affected zone located behind the breastwork. The surface erosion is higher in samples implanted with helium: more intense material boiling inside the hole, the formation of a breastwork in the form of an annular rim, and the formation of areas of three types in the heat-affected zone are observed. It is found that the microhardness of the alloy surface after He⁺ ion implantation and in the holes formed under subsequent exposure to laser radiation practically does not change (within the measurement error) and the microhardness in the holes of the original alloy first decreases when exposed to laser radiation, and then with an increase in the number of pulses, there is a tendency to its increase. The mechanisms of the observed phenomena are discussed.

The effect of the structural state of a deformable aluminum alloy on its wear resistance under high sliding speed conditions has been experimentally studied. Equal-channel angular pressing method was used to form different structural states in the AMg6 alloy. The formation of an ultrafine-grained state of the samples was established using transmission electron microscopy. It was found that a change in the structure made it possible to increase the mechanical properties under tension and nanohardness of the AMg6 alloy. To study the tribological properties, tests were performed under dry friction conditions with different sliding speeds. The ultrafine-grained state was experimentally established to contribute to a decrease in the friction coefficient. The sliding speed and structural state affect the wear intensity of the studied samples. It was shown that tribooxidation of the sample surface is a mechanism for increasing the wear resistance of the AMg6 alloy. It was found that the sliding speed affects the formation of the surface layer and deformation in the near-surface zone in the studied samples. Oscillations of the tribological system have been studied by analyzing the vibration amplitude. It was established that the formation of the ultrafine-grained structure helps to reduce oscillations in the tribological system. The change in the parameters of acoustic emission signals depending on the sliding speed and structural state of the samples has been studied. A correlation has been revealed between wear indicators and dynamic characteristics of the tribosystem.